1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, and more particularly to an electrode structure of the device for use in semiconductor memories, photoelectric transducers, signal processors and so on which are mounted on various electronic equipment such as copying machines, facsimile apparatus, printers, silver salt cameras, video tape recorders and image displays and, though small in size, considerably affect specifications of the equipment.
2. Related Background Art
In electronic devices and integrated circuit elements each using semiconductors, aluminum (Al), aluminum containing silicon (Al-Si) or the like have been conventionally employed to form electrodes and wirings (conductor patterns). Al has many advantages that it is cheap and exhibits high electric conductivity, can chemically protect and stabilize the interior because of a dense oxide film formed on the surface, and has good adhesivity with Si.
Meanwhile, in recent years, an increased degree of integration of integrated circuits like LSIs has particularly required a decrease of the wire or conductor size and multiple layers of wirings, thereby in turn imposing so strict demands as have not been experienced so far on the wirings. In dynamic RAMs of 4 Mbit and 16 Mbit, for example, the aspect ratio (i.e., opening depth/opening diameter) of an opening (so-called beer hole) in which a metal like Al must be deposited is more than 1.0. Also, the opening diameter itself is below 1 .mu.m. This necessitates a technique which can deposit Al even in openings having the large aspect ratio.
Additionally, in order to achieve commerical success, semiconductor integrated circuit devices must be mass-produced at the low production cost.
To date, there have been known, as methods of forming metal films like Al films, a sputtering process and a vapor phase process such as a CVD (Chemical Vapor Deposition) process using trimethylaluminum (TMA). Above all, the thermal CVD process has been researched from wide and various angles. One example is to disperse organic aluminum in carrier gas for transporting it over a heated substrate, so that gas molecules are thermally decomposed on the substrate to form a film. As described in Journal of Electrochemical Society, Vol. 131, p. 2175 (1984), by way of example, triisobutylaluminum (i-C.sub.4 H.sub.9).sub.3 Al(TIBA) is used as organic aluminum gas to form a film of 3.4 .mu..OMEGA..cm at the film forming temperature of 260.degree. C. and the reaction tube pressure of 0.5 Torr,
However, the above method is so poor in surface flatness of Al as not to provide a film of good quality from the standpoints of step coverage and electro migration. In addition, Al deposited in openings is not dense.
Further, Japanese Patent Laid-Open No. 63-33569 discloses a method of forming a film by heating organic aluminum in the vicinity of a substrate. This method enables to selectively deposit Al by the CVD process only on those surface areas of a metal or semiconductor from which the natural surface oxide film has been removed away. With the disclosed method, after filling openings, Al is deposited on the oxide film by the sputtering process.
That method also has, however, a disadvantage that since surface flatness of Al in openings, as major basic condition for a good film, electric contact at the interface between the Al film formed by the CVD process and the Al film formed by the sputtering process is poor, which in turn increases resistivity.
As a modified example, a double-wall CVD process is described in Proceedings of 2nd Symposium by Japanese Branch of Electrochemical Society, (Jul. 7, 1989), p. 75. While this process enables to selectively grow Al only on metals or semiconductors using TIBA gas, it is disadvantageous in that difficulties are encountered in precise control of a difference between the gas temperature and the substrate surface temperature, and that both a bomb and a pipe must be heated.
Stated otherwise, an attempt of controlling the above temperature difference complicates production apparatus and thus necessarily leads to a single-substrate processing type that can deposite Al on only one wafer for each deposition process. Moreover, the modified method can only produce a film, which is never said as being of good quality, at a deposition rate of 500 .ANG./min at maximum and thus cannot realize a throughput necessary for mass production. In addition, the film formed by the modified method does not become a uniform and continuous film unless it is deposited up to some thickness. The formed film is also unsatisfactory in reproducibility and insufficient for mass production because film flatness is poor and selectivity needed in selective growth of Al will not last for a so long time.
Thus, in the conventional methods, since a metal is not sufficiently filled in contact holes or the like which are partially exposed to an insulating film, the filled metal cannot be said as being of good quality in itself, thereby causing an increase of the wire resistance, a wire breakage and other troubles. An attempt of preventing such shortcomings inevitably increases thicknesses of Al films and inter-layer insulating films, which is contrary to a direction toward improved flatness necessary for a reduction in the element size and a higher degree of integration. This has in turn adversely affected not only performance of semiconductor devices but also yield of production to a large extent.
Even with the filled metal being of good quality and having satisfactory selectivity, if wiring material interconnecting filled lead-out electrodes is aluminum-base material such as aluminum or an alloy containing aluminum as a main ingredient, wiring characteristics are deteriorated due to stress migration or electro migration. In this respect, therefore, a further improvement has been demanded. It has also been desired to obtain other wiring material having lower resistance than an aluminum-base metal.
In summary, the conventional CVD processes have suffered from the problem that an improvement in the deposition rate and output, which is essential to mass production of semiconductor integrated circuit devices at the low cost, cannot be expected and satisfactory selective growth of Al cannot be realized. Even if satisfactory selective growth of Al is obtained, there still remain problems in flatness, purity, step coverage and dense filling of Al into contact holes, meaning poor reproducibility. In other words, there have been left many points to be improved for a higher degree of integration.